It has been described by T. E. Sharp, J. R. Eyler and E. Li in Int. J. Mass Spectr. Ion Phys. 9 (1972) 421, for example, that the effective cyclotron resonance frequency .omega..sub.eff is not identical with the true cyclotron resonance frequency .omega..sub.c, which is equal to the product of the charge-to-mass ratio q/m and the magnetic field strength B. Rather, the effective cyclotron resonance frequency is a function of the true cyclotron resonance frequency .omega..sub.c and the frequency .omega..sub.t of oscillations of the ions in the direction of the magnetic field inside the trapped ion cell. The latter frequency, in turn, depends on the potentials applied to the trapped ion cell, the geometry of the trapped ion cell and, again, the charge-to-mass ratio. The complex functions involved necessitate the creation of a calibration curve for each spectrometer and require frequent repetition of the calibration procedure because of variations in the electric fields inside the trapped ion cell, particularly in terms of time, which are prone to lead to alterations in the calibration curve.
It is also a disadvantage that the functional relationship between the effective resonance frequency .omega..sub.eff and the charge-to-mass ratio is very complicated so that a great number of calibration points are required to produce a sufficiently accurate curve. Attempts made heretofore to find approximations suitable for producing calibration curves have proven unsatisfactory so far. Thus, Ledford et al., for example, use a calibration function with three parameters; this function, however, yields an accuracy of only 3 ppm in the very small range of mass-to-charge ratio of 117 to 135 (Anal. Chem. 52 (1980) 463).